Theorem expi 141

Description: An exportation inference. (Contributed by NM, 5-Aug-1993.) (Proof shortened by O'Cat, 28-Nov-2008.)

Hypothesis

Ref	Expression
expi.1	|- (-. (ph -> -. ps) -> ch)

Assertion

Ref	Expression
expi	|- (ph -> (ps -> ch))

Proof of Theorem expi

Step	Hyp	Ref	Expression
1		pm3.2im 137	. 2 |- (ph -> (ps -> -. (ph -> -. ps)))
2		expi.1	. 2 |- (-. (ph -> -. ps) -> ch)
3	1, 2	syl6 29	1 |- (ph -> (ps -> ch))

This proof depends on syntax axioms:  -. wn 3   -> wi 4

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem is used by:  bi3  179  ex  423